The useful part of the spectrum for wireless telecommunications is limited and is therefore an expensive commodity that cellular operators have spent large amounts on. As a result, they have a high interest in utilizing the spectrum as efficiently as possible.
There are different approaches that can be used to increase the efficiency of spectrum use. Some examples are small cells, which are low-powered radio access nodes that can be used to offload traffic, multiple-input and multiple-output (MIMO) antennas, and improved data coding and modulation techniques.
Using different frequency bands for transmission and reception was taken as given since the early beginnings of wireless communications, and not questioned much. However, recently, techniques to successfully receive and transmit signals simultaneously in the same frequency bands of operation have been proposed. Frequency resource allocation schemes can enable full-duplex communications in homogeneous macro-cellular networks, but a new type of physical layer interference emerges due to full-duplex communications, that is the inter-link interference between downlink (DL) and uplink (UL) transmissions, which can be an issue in heterogeneous and small cell networks.